Pipeline must sometimes be installed under physical barriers such as waterways and buildings or other surface obstructions without disturbing the surface. Typically, this has been done through a process of drilling a pilot bore beneath the surface barrier along a preselected, partially arcuate path. Next, the pilot bore is usually reamed to a larger size as required for the planned services. A pipe line drilling rig is used for this purpose. The rig is mounted on an inclined ramp and includes a rotary drive with hydraulic means for moving the rotary drive up and down the length of the ramp to advance or withdraw the drill string. The ramp is typically provided as the deck of a flat bed trailer, equipped with tracks and a hydraulically powered chain drive mechanism for movement of the rotary drive. The trailer is spotted and dropped nose down on one side of the barrier. The rig is made ready to start drilling stabilizing the trailer deck with hydraulic outriggers and adjusting the ramp angle of inclination as desired for the hole to be drilled. The drill pipe comes in threaded lengths of from twenty-five to thirty-nine feet and generally, an excavating machine is pressed into service to be used as a crane for handling these pipe lengths. The process generally starts with digging a trench, so that the drill bit can bear perpendicularly against the surface where the hole is to enter. The trench also provides a pit for holding the large quantity of drilling mud normally required. As rotary drilling advances the hole, lengths of pipe are added to the drill string until the length planned for the initial tangent is reached. The pipe string is then pulled out of the hole so that a mud-powered drill motor can be installed in place of the rotary drill bit. The mud-powered drill motor is mounted with its drilling axis angularly offset from the drill string axis by approximately 2.degree., so as to cause the drill to advance along a predictable arcuate path. The drill motor is positioned with its angularly offset axis oriented upward. Thus positioned, running the drill motor and advancing the drill string by axial hydraulic force only, without drill string rotation, generates an upwardly curving hole. Since the radius of hole curvature is predictable, calculations can determine the additional length of drill pipe needed to bring the hole to the surface or to make a transition to a predetermined tangent for reaching the surface. The bore has a larger diameter than the drill pipe for drilling fluid or "mud" circulation. This allows cuttings to be removed from the hole by mud circulation through the drill pipe, across the cutting face, through the open annulus and back to the surface.
Starting a straight "horizontal" hole can be difficult, especially if the entry point is more than a few feet from the end of the trailer, because the drill pipe tends to droop under its own weight. Physical considerations, such as the size and location of the trench and mud pit, often dictate an entry point twenty-five feet or more from the end of the trailer. In these cases, starting a straight hole is particularly difficult and it is important to get the hole started straight in order to follow a predictable path.
Unlike in vertical drilling, where drill string weight crowds the drilling tool against the cutting surface, the crowding force in this type of more or less horizontal drilling must be applied by pushing on the drill string. As the hole gets longer, the drill string reaches a length where it is unstable under the necessary column load, so that it deflects and bears randomly against the side of the hole. This deflected, off-center pipe can also cause whipping between the rotary drive and the hole entry point. Fluted members called stabilizers, sized to pass through the bore diameter with minimal clearance, are fitted to the drill string at intervals. The stabilizers center the drill string in the bore and help in holding direction as the hole progresses. The stabilizers also help to control pipe whipping.
Another problem peculiar to horizontal drilling is the difficulty in supporting the pipe to hold the male and female threaded ends in axial and angular alignment as lengths are added to or removed from the pipe string. This problem is worsened by increasing droop as the unsupported pipe length between the end of the ramp and the entry point increases.
Therefore, a first object of the present inventions is to provide apparatus for guiding the drill pipe so as to facilitate drilling a straight hole at entry. A second object is that this apparatus prevent drill pipe "whipping" by keeping it centered while drilling. A third object is that this apparatus facilitate re-entry of the hole when the drill pipe has been pulled out. A fourth object is that this apparatus be capable of supporting the drill pipe between the hole and the end of the inclined ramp so that the threaded end is held in alignment with the rotary drive while pipe is added to or removed from the drill string and yet another object is that this apparatus be made in a form that does not interfere with the normal coupling of a trailer mounted horizontal drilling rig.